A floating microwave filter in a waveguide structure has been described in particular in patent document U.S. Pat. No. 4,990,870.
Conventional microwave filters in a waveguide structure use filtering elements that are in electrical and mechanical contact with the walls of the waveguide. In a technology known as “Finline” or a technology called “E plane”, resonant metal features are etched either in a thin dielectric substrate or directly in a metal foil. This etched substrate or foil is then attached in the E plane of a rectangular waveguide, which ensures perfect positioning of the substrate or foil in the waveguide and perfect electrical continuity between the metal walls of the waveguide and the metallized portions of the substrate or foil.
In a floating microwave filter in a waveguide structure, the filtering elements are not in electrical and mechanical contact with the walls of the waveguide.
The floating microwave filter in a waveguide structure known from the aforementioned document is assembled by inserting a printed circuit mounted on the back of a foam bar into a metal waveguide of rectangular cross section and in a plane parallel to the short side of the cross section of the waveguide, which simplifies the assembly technique compared to that of a conventional filter and reduces the production costs. Moreover, a floating microwave filter in a waveguide structure has, compared with a conventional filter, improved characteristics as regards insertion losses.